Agriculture currently uses 70 per cent of the freshwater available for human use and, according to the IWMI, unless there is a huge leap in water-use efficiency on farms worldwide, a 70 or 100 per cent increase in food production will require roughly twice the amount of water in use today.

'The numbers don’t add up,' said IWMI Deputy director Colin Chartres, 'That amount of additional water just isn’t there. In fact, because of rising demand for water in other sectors, agriculture will have to produce more food with even less water.' Water warnings

A number of recent reports have emphasised the threat of water scarcity. The Lloyds insurance group warned that water stress was leading to price instability in agricultural markets. It said the record sugar price levels in August 2009 were in part a response to the projections of weaker monsoons in India and irregular rains in Brazil.

It also highlighted South Asia as a particular hotspot where, 'over-exploitation of water resources is being driven by a high population density, climate variability, hydropower requirements, poor water governance and widespread ecological collapse of freshwater systems'.Water Productivity

Chartres said water availability was being 'overlooked' by agronomists when they were looking at increasing yields or, in some cases, assumed to be 'infinitely available'.

He said governments and advocacy groups like the Soil Association should focus more on ways of improving water management practices in agriculture.

'The issue here is that we should be trying to optimise water productivity (yield per unit volume of water applied or evapotranspirated) for all production systems. In some countries small farms are more productive than larger ones, but in others large and intensive systems perform better,' said Chartres.

The IWMI said more precise water delivery could make irrigation more efficient while water rationing and pricing could persuade farmers to reduce consumption. It also recommended governments should promote agricultural trade from water abundant and water efficient regions to water scarce areas and also influence diets toward more water-efficient foods.

'It is not the amount of water that is lacking globally. Rather we are lacking in good management of water and land resources,' said IWMI director David Molden in a recent speech on water scarcity.